query on QCoreApplication::exec

[psadhukhan]

Hi,

From http://doc.trolltech.com/4.4/threads.html, I found that
Note that QCoreApplication::exec() must always be called from the main thread (the thread that executes main()), not from a QThread. In GUI applications, the main thread is also called the GUI thread because it's the only thread that is allowed to perform GUI-related operations.

but in the attached application, I tried creating a linux thread from main and tries to call exec from the spawned thread and exec works.
I guess as per above line, exec() should only be calling from thread running main() and not from the spawned thread, am I right?
My question is is any thread a main thread (even though it's not running main()) and therefore can call exec() so long it's not spawned by QThread api?

#include <pthread.h>
#include <Qt>
#include <QtCore>
#include <QtGui>
#include <QPainter>
#include <QWidget>
#include <QImage>
 
class QPen;
class QBrush;
class QImage;
 
#define SCREEN_X_RESOLUTION 800
#define SCREEN_Y_RESOLUTION 600
 
struct qtimagedesc {
	QPaintDevice *qpd;
};
typedef struct qtimagedesc QtImageDesc;
 
QtImageDesc *QtImageDescPool = NULL;
bool initDone = false;
 
#define qtApp	((QtApplication *)qApp)
void threadfunc(void *arg);
void AWT_drawline(int x1, int y1, int x2, int y2);
void AWT_drawrect(int x, int y, int w, int h);
void getQtColorModel();
void Qtexec();
 
 
QImage img(SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION,QImage::Format_ARGB32);
 
class QtWindow : public QWidget
{
       QBitmap transMask;
 
public:
        QtWindow(int flags,
		const char *name = "Sun AWT/Qt",
             QWidget *parent = NULL) ;
	virtual void setMask(const QBitmap &);
	virtual void paintEvent(QPaintEvent *);
 
};
 
class QtApplication : public QApplication {
public :
	QtApplication(int &argc, char **argv);
	int exec(); //overloadded exec from QApplication
};
 
class QtScreen
{
protected :
    int m_x;
    int m_y;
    int m_width;
    int m_height;
    QtWindow *m_window;
    bool m_bounds_restricted;
/*    virtual char **getArgs(int *argc);
    virtual void computeBounds();
    virtual void createQtWindow();
    virtual void windowShown();
*/
 
public :
    QtScreen();
    bool init();
 /*   void close();
    void showWindow();
    void setMouseCursor(int cursor);
    void beep();
    int width();
    int height();
    int dotsPerInch();
    QtWindow *window();
    int x();
    int y();
*/
};
 
class QtScreenFactory
{
	static QtScreen *theScreen;
public:
	static QtScreen *getScreen();
};
 
 
QtWindow *m_window;
QtScreen *QtScreenFactory::theScreen = NULL;
QtApplication::QtApplication(int &argc, char **argv) : QApplication(argc, argv) {
}
 
int
QtApplication::exec(void) {
	printf("QApplication exec called %x\n", pthread_self());
	QApplication::exec();
	printf("QApplication exec done\n");
}
 
QtWindow::QtWindow(int flags, const char *name, QWidget *parent) :
	QWidget(parent, (Qt::WindowFlags)flags)
{
	setMouseTracking(true);
}
 
void QtWindow::setMask(const QBitmap &bm)
{
	printf("QtWindow::setMask\n");
}
 
void
QtWindow::paintEvent(QPaintEvent *event)
{
	printf("paintEvent called\n");
#if 0
	QPen *qp = new QPen();
	QColor c(0xffff0000);
	qp->setColor(c);
	QBrush *qb = new QBrush();
	QPainter p(this);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	p.setPen(*qp);
	p.setClipRect(0,0,800,600);
	p.drawLine(30,135,790,135);
#endif
	QPainter p(QtImageDescPool[0].qpd);
	QPoint pt(0,0);
	p.drawImage(pt, img);
}
 
int main(int argc, char **argv)
{
	pthread_t tid;
	printf("main thread %x, argc %d, argv %s\n",pthread_self(), argc, *argv);
#if 1
	pthread_create(&tid, NULL, (void *(*)(void *))threadfunc, NULL);
#endif
	while(!initDone);
	AWT_drawline(0,599,799,599);
	usleep(1000);
	AWT_drawrect(30,135,190,100);
	while(true) {}
//	 img = new QImage(800,600,QImage::Format_ARGB32);
}
 
QtScreen *
QtScreenFactory::getScreen() {
	printf("QtScreenFactory::getScreen()\n");
	if ( QtScreenFactory::theScreen == NULL ) {
        QtScreenFactory::theScreen = new QtScreen();
    	    if(QtScreenFactory::theScreen != NULL) {
	    	    QtScreenFactory::theScreen->init();
			}
	}
	return QtScreenFactory::theScreen;
}
 
QtScreen::QtScreen()
{
	printf("QtScreen::QtScreen()\n");
	QtImageDescPool = (QtImageDesc *) calloc(sizeof(QtImageDesc), 128);	
}
 
void getQtColorModel()
{
	int depth = 0;
	int amask=0,rmask=0,gmask=0,bmask=0;
 
	QWidget *d = QApplication::desktop();
	depth = d->depth();	
	printf ("Depth = %d\n", depth);
	switch(depth) {
		case 32:
			amask = 0xff000000;
		case 24:
			rmask = 0x00ff0000;
			gmask = 0x0000ff00;
			bmask = 0x000000ff;
				break;
	}
}
 
void Qtexec()
{
	qtApp->exec();
}
 
bool
QtScreen::init()
{
	printf("QtScreen::init() %x\n", pthread_self());
	int m_x = 0,m_y=0,m_width=SCREEN_X_RESOLUTION,m_height=SCREEN_Y_RESOLUTION;
 
	int argc = 1;
//	char *argv[3] = {"a.out", "-qws", NULL};
 
	char **argv = (char**)malloc(sizeof(char**) * 2);
	argv[0] = (char *)malloc(sizeof(char) * 128);
	argv[1] = NULL;
	strcpy(argv[0], "cvm");
 
	new QtApplication(argc, argv);
	QRect screen_bounds = QApplication::desktop()->frameGeometry();
	m_window = new QtWindow(Qt::FramelessWindowHint|Qt::Window);
	printf("m_window %x\n", this->m_window);
	QBitmap bitmap(m_width, m_height);
	m_window->setMask(bitmap);
	qtApp->setActiveWindow(this->m_window);
	this->m_window->move(0,0);
	this->m_window->setFixedSize(SCREEN_X_RESOLUTION, SCREEN_Y_RESOLUTION);
	this->m_window->show();
 
	QtImageDescPool[0].qpd = this->m_window;
 
	getQtColorModel();
	initDone = true;
 
}
 
 
void threadfunc(void *arg)
{
	printf("threadfunc called\n");
	QtScreen *screen = QtScreenFactory::getScreen();
				Qtexec();
}
 
void
AWT_drawline(int x1, int y1, int x2, int y2)
{
#if 0
	QPen *qp = new QPen();
	QBrush *qb = new QBrush();
	QPainter p(qpd);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	p.setPen(*qp);
	p.setClipRect(0,0,800,600);
	p.drawLine(30,135,790,135);
#endif
	printf("drawline called\n");
	QPainter p(&img);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	QPen *qp = new QPen();
	QColor c(0xffff0000);
	qp->setColor(c);
	QBrush *qb = new QBrush();
	p.setPen(*qp);
	p.setClipRect(0,0,SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION);
	p.drawLine(x1, y1, x2, y2);
	printf("m_window %x\n", ((QtWindow *)QtImageDescPool[0].qpd));
	//((QtWindow *)arg)->update(0,0,800,600);
	((QtWindow *)QtImageDescPool[0].qpd)->update(0,0,SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION);
}
 
void
AWT_drawrect(int x, int y, int w, int h)
{
	printf("drawrect called\n");
	QPainter p(&img);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	QPen *qp = new QPen();
	QColor c(0xffff0000);
	qp->setColor(c);
	p.setPen(*qp);
	p.setClipRect(0,0,800,600);
	p.drawRect(x, y, w, h);
	printf("m_window %x\n", ((QtWindow *)QtImageDescPool[0].qpd));
	//((QtWindow *)arg)->update(0,0,800,600);
	((QtWindow *)QtImageDescPool[0].qpd)->update(0,0,SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION);
}

#include <pthread.h>
#include <Qt>
#include <QtCore>
#include <QtGui>
#include <QPainter>
#include <QWidget>
#include <QImage>

class QPen;
class QBrush;
class QImage;

#define SCREEN_X_RESOLUTION 800
#define SCREEN_Y_RESOLUTION 600

struct qtimagedesc {
	QPaintDevice *qpd;
};
typedef struct qtimagedesc QtImageDesc;

QtImageDesc *QtImageDescPool = NULL;
bool initDone = false;

#define qtApp	((QtApplication *)qApp)
void threadfunc(void *arg);
void AWT_drawline(int x1, int y1, int x2, int y2);
void AWT_drawrect(int x, int y, int w, int h);
void getQtColorModel();
void Qtexec();


QImage img(SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION,QImage::Format_ARGB32);

class QtWindow : public QWidget
{
       QBitmap transMask;

public:
        QtWindow(int flags,
		const char *name = "Sun AWT/Qt",
             QWidget *parent = NULL) ;
	virtual void setMask(const QBitmap &);
	virtual void paintEvent(QPaintEvent *);

};

class QtApplication : public QApplication {
public :
	QtApplication(int &argc, char **argv);
	int exec(); //overloadded exec from QApplication
};

class QtScreen
{
protected :
    int m_x;
    int m_y;
    int m_width;
    int m_height;
    QtWindow *m_window;
    bool m_bounds_restricted;
/*    virtual char **getArgs(int *argc);
    virtual void computeBounds();
    virtual void createQtWindow();
    virtual void windowShown();
*/

public :
    QtScreen();
    bool init();
 /*   void close();
    void showWindow();
    void setMouseCursor(int cursor);
    void beep();
    int width();
    int height();
    int dotsPerInch();
    QtWindow *window();
    int x();
    int y();
*/
};

class QtScreenFactory
{
	static QtScreen *theScreen;
public:
	static QtScreen *getScreen();
};


QtWindow *m_window;
QtScreen *QtScreenFactory::theScreen = NULL;
QtApplication::QtApplication(int &argc, char **argv) : QApplication(argc, argv) {
}

int
QtApplication::exec(void) {
	printf("QApplication exec called %x\n", pthread_self());
	QApplication::exec();
	printf("QApplication exec done\n");
}

QtWindow::QtWindow(int flags, const char *name, QWidget *parent) :
	QWidget(parent, (Qt::WindowFlags)flags)
{
	setMouseTracking(true);
}

void QtWindow::setMask(const QBitmap &bm)
{
	printf("QtWindow::setMask\n");
}
	
void
QtWindow::paintEvent(QPaintEvent *event)
{
	printf("paintEvent called\n");
#if 0
	QPen *qp = new QPen();
	QColor c(0xffff0000);
	qp->setColor(c);
	QBrush *qb = new QBrush();
	QPainter p(this);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	p.setPen(*qp);
	p.setClipRect(0,0,800,600);
	p.drawLine(30,135,790,135);
#endif
	QPainter p(QtImageDescPool[0].qpd);
	QPoint pt(0,0);
	p.drawImage(pt, img);
}

int main(int argc, char **argv)
{
	pthread_t tid;
	printf("main thread %x, argc %d, argv %s\n",pthread_self(), argc, *argv);
#if 1
	pthread_create(&tid, NULL, (void *(*)(void *))threadfunc, NULL);
#endif
	while(!initDone);
	AWT_drawline(0,599,799,599);
	usleep(1000);
	AWT_drawrect(30,135,190,100);
	while(true) {}
//	 img = new QImage(800,600,QImage::Format_ARGB32);
}

QtScreen *
QtScreenFactory::getScreen() {
	printf("QtScreenFactory::getScreen()\n");
	if ( QtScreenFactory::theScreen == NULL ) {
        QtScreenFactory::theScreen = new QtScreen();
    	    if(QtScreenFactory::theScreen != NULL) {
	    	    QtScreenFactory::theScreen->init();
			}
	}
	return QtScreenFactory::theScreen;
}

QtScreen::QtScreen()
{
	printf("QtScreen::QtScreen()\n");
	QtImageDescPool = (QtImageDesc *) calloc(sizeof(QtImageDesc), 128);	
}

void getQtColorModel()
{
	int depth = 0;
	int amask=0,rmask=0,gmask=0,bmask=0;

	QWidget *d = QApplication::desktop();
	depth = d->depth();	
	printf ("Depth = %d\n", depth);
	switch(depth) {
		case 32:
			amask = 0xff000000;
		case 24:
			rmask = 0x00ff0000;
			gmask = 0x0000ff00;
			bmask = 0x000000ff;
				break;
	}
}

void Qtexec()
{
	qtApp->exec();
}

bool
QtScreen::init()
{
	printf("QtScreen::init() %x\n", pthread_self());
	int m_x = 0,m_y=0,m_width=SCREEN_X_RESOLUTION,m_height=SCREEN_Y_RESOLUTION;

	int argc = 1;
//	char *argv[3] = {"a.out", "-qws", NULL};

	char **argv = (char**)malloc(sizeof(char**) * 2);
	argv[0] = (char *)malloc(sizeof(char) * 128);
	argv[1] = NULL;
	strcpy(argv[0], "cvm");

	new QtApplication(argc, argv);
	QRect screen_bounds = QApplication::desktop()->frameGeometry();
	m_window = new QtWindow(Qt::FramelessWindowHint|Qt::Window);
	printf("m_window %x\n", this->m_window);
	QBitmap bitmap(m_width, m_height);
	m_window->setMask(bitmap);
	qtApp->setActiveWindow(this->m_window);
	this->m_window->move(0,0);
	this->m_window->setFixedSize(SCREEN_X_RESOLUTION, SCREEN_Y_RESOLUTION);
	this->m_window->show();

	QtImageDescPool[0].qpd = this->m_window;
	
	getQtColorModel();
	initDone = true;
	
}


void threadfunc(void *arg)
{
	printf("threadfunc called\n");
	QtScreen *screen = QtScreenFactory::getScreen();
				Qtexec();
}

void
AWT_drawline(int x1, int y1, int x2, int y2)
{
#if 0
	QPen *qp = new QPen();
	QBrush *qb = new QBrush();
	QPainter p(qpd);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	p.setPen(*qp);
	p.setClipRect(0,0,800,600);
	p.drawLine(30,135,790,135);
#endif
	printf("drawline called\n");
	QPainter p(&img);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	QPen *qp = new QPen();
	QColor c(0xffff0000);
	qp->setColor(c);
	QBrush *qb = new QBrush();
	p.setPen(*qp);
	p.setClipRect(0,0,SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION);
	p.drawLine(x1, y1, x2, y2);
	printf("m_window %x\n", ((QtWindow *)QtImageDescPool[0].qpd));
	//((QtWindow *)arg)->update(0,0,800,600);
	((QtWindow *)QtImageDescPool[0].qpd)->update(0,0,SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION);
}

void
AWT_drawrect(int x, int y, int w, int h)
{
	printf("drawrect called\n");
	QPainter p(&img);
	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	QPen *qp = new QPen();
	QColor c(0xffff0000);
	qp->setColor(c);
	p.setPen(*qp);
	p.setClipRect(0,0,800,600);
	p.drawRect(x, y, w, h);
	printf("m_window %x\n", ((QtWindow *)QtImageDescPool[0].qpd));
	//((QtWindow *)arg)->update(0,0,800,600);
	((QtWindow *)QtImageDescPool[0].qpd)->update(0,0,SCREEN_X_RESOLUTION,SCREEN_Y_RESOLUTION);
}

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[psadhukhan]

I also saw that from QCoreApplication::exec() that

int QCoreApplication::exec()
{
    if (!QCoreApplicationPrivate::checkInstance("exec"))
        return -1;
 
    QThreadData *threadData = self->d_func()->threadData;
    if (threadData != QThreadData::current()) {
        [B]qWarning("%s::exec: Must be called from the main thread",[/B] self->metaObject()->className());
        return -1;
    }
    if (!threadData->eventLoops.isEmpty()) {
        qWarning("QCoreApplication::exec: The event loop is already running");
        return -1;
    }

int QCoreApplication::exec()
{
    if (!QCoreApplicationPrivate::checkInstance("exec"))
        return -1;

    QThreadData *threadData = self->d_func()->threadData;
    if (threadData != QThreadData::current()) {
        [B]qWarning("%s::exec: Must be called from the main thread",[/B] self->metaObject()->className());
        return -1;
    }
    if (!threadData->eventLoops.isEmpty()) {
        qWarning("QCoreApplication::exec: The event loop is already running");
        return -1;
    }

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that it will throw an warning as shown above if not called from main thread but I did not get any warning, so I guess any thread can call exec() so long the thread also does QApplication(argc, argv) and it's not spawned by QThread api?
Can you please confirm?